Canvas，中文翻譯為“畫布”，HTML5中新增了元素，可以結合JavaScript動態地在畫布中繪製圖形。本文我們就和大家分享javaScript canvas實作(畫筆大小 顏色 橡皮擦的實例)，具有很好的參考價值，希望對大家有幫助。 實例如下所示： # shape rectangle circle line var shap = 99; //0 is circle; 1 is rectangle var orignalX, orignalY;//the coordinate of mouse down var lastX, lastY;//the coordinate of last mouse position var isMouseDown = false; // flag of mouse pressing down var myCanvas = document.getElementById("myCanvas"); var context = myCanvas.getContext('2d'); var width = myCanvas.width, height = myCanvas.height; var data;//storing last canvas' content context.strokeStyle = "black"; context.strokeWidth=1; context.lineWidth = 1; document.getElementById('color').onchange = function(){ context.strokeStyle = this.value }; function doEraser(){ context.strokeStyle = "white"; shap = 2; } function sizeChange(){ context.lineWidth = parseInt(document.getElementById('size').value); } function shapeChange(){ context.strokeStyle = "black"; var myselect = document.getElementById("shape"); var index=myselect.selectedIndex ; var myvalue = myselect.options[index].value; var mytext=myselect.options[index].text; shap = parseInt(myvalue); } function myCanvasMouseDown(event) { //event.preventDefault(); if(event.button == 0) { orignalX = event.offsetX; orignalY = event.offsetY; context.moveTo(orignalX,orignalY); data = context.getImageData(0, 0, width, height); isMouseDown = true; } } function myCanvasMouseMove(event) { if (isMouseDown){ //event.preventDefault(); switch(shap){ case 0: context.clearRect(0,0,width,height); context.putImageData(data,0,0); lastX = event.offsetX; lastY = event.offsetY; context.beginPath(); context.arc(orignalX+(lastX-orignalX)/2,orignalY+(lastY-orignalY)/2,Math.abs(lastX-orignalX)/2,0,Math.PI * 2,true); context.stroke(); context.closePath(); break; case 1: context.clearRect(0,0,width,height); context.putImageData(data,0,0); lastX = event.offsetX; lastY = event.offsetY; context.strokeRect(orignalX, orignalY, lastX-orignalX, lastY-orignalY); break; case 2: lastX = event.offsetX; lastY = event.offsetY; context.lineTo(lastX, lastY); //根据鼠标路径绘画 context.stroke(); //立即渲染 break; } } } function myCanvasMouseUp(event) { if (isMouseDown){ //event.preventDefault(); context.clearRect(0,0,width,height); context.putImageData(data,0,0); lastX = event.offsetX; lastY = event.offsetY; switch(shap){ case 0: context.beginPath(); context.arc(orignalX+(lastX-orignalX)/2,orignalY+(lastY-orignalY)/2,Math.abs(lastX-orignalX)/2,0,Math.PI * 2,true); context.stroke(); context.closePath(); break; case 1: context.beginPath(); context.strokeRect(orignalX, orignalY, lastX-orignalX, lastY-orignalY); context.closePath(); break; case 2: context.lineTo(lastX, lastY); //根据鼠标路径绘画 context.stroke(); //立即渲染 break; } isMouseDown = false; lastX = null; lastY = null; orignalX = null; orignalY = null; data = context.getImageData(0, 0, width, height); context.beginPath(); context.clearRect(0,0,width,height); context.putImageData(data,0,0); context.closePath(); } } myCanvas.addEventListener("mousedown", myCanvasMouseDown, false); myCanvas.addEventListener("mousemove", myCanvasMouseMove, false); myCanvas.addEventListener("mouseup", myCanvasMouseUp, false); 登入後複製 相關推薦： Canvas處理圖片的方法 HTML5裡Canvas常用的繪圖技巧 js+HTML5使用canvas繪製圖片方法詳解
